Mirror Frequency (Frequency)

Default: cleared

Use Mirror Frequency when measuring a signal that is mirrored to display the signal unmirrored.

Selected: The displayed frequency spectrum is mirrored (flipped) about the VSA center frequency.

Cleared: Does not mirror the frequency spectrum.

This feature is available only for zoomed measurements, not for baseband.

External downconverter

If an external downconverter is being used, clear this Mirror Frequency check box and use the Spectrum parameter in the Frequency Converter section of the User Correction dialog box instead.

Mirror frequency concepts

Often when a signal is mixed down from a higher frequency, the spectrum is flipped or mirrored about the center frequency as a result of the mixing scheme used. A mirrored spectrum occurs when both the mixer input frequency and the mixer output frequency are lower than the mixer LO frequency. A mirrored spectrum may also occur in two channel I+jQ measurements if the channels are swapped.

Many RF Radio Frequency: A generic term for radio-based technologies, operating between the Low Frequency range (30k Hz) and the Extra High Frequency range (300 GHz). and microwave spectrum VSAs perform their first frequency conversion in bands. The mixing scheme for each band may be different--the spectrum may be mirrored in some bands but not in others.

To get the correct display of a flipped spectrum, select the Mirror Frequency check box.

When the Mirror Frequency check box is selected, the marker readings and frequency annotation are now reversed with respect to the physical signal being input to the hardware.

Digital demodulated signals

If using Digital Demodulation (Digital Demodulator is selected), there is a Mirror Frequency Spectrum parameter in demod properties. This parameter can be used if there is a baseband modulator that inverts the signal. When the demod Mirror Frequency Spectrum is selected, the mirroring occurs in the digital demodulator rather than in time corrections as shown below. This parameter does not change the displayed spectrum trace data. If you want to correctly demodulate and display mirrored spectrums, use the Mirror Frequency parameter (Meas Setup) instead of the Digital Demod Properties Mirror Frequency Spectrum.

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